im running win 7 with a core-2 quad and 4 gigs of ddr3.. 768m 9700GSO gforce.  I should have no vid lag and dont in other games of compareable graphics. I get it in both win mode and fullscreen. (perfer win mode -- run 2 accts)  not all the time but it does seem to build up when it does.. I lean twords the mem leak theory, but hasnt brought me to a total crash.
(its happened when running only one account too)